# stayOnlyVariable <- function(obj, lst, coln) {
#   ss <- getSlots(class(obj))
#   ss <- names(ss)[ss == "data.frame"]
#   ss <- ss[sapply(ss, function(x) (any(colnames(slot(obj, x)) == coln) && nrow(slot(obj, x)) != 0))]
#   for (sl in ss) {
#     slot(obj, sl) <- slot(obj, sl)[is.na(slot(obj, sl)[, coln]) | slot(obj, sl)[, coln] %in% lst, , drop = FALSE]
#   }
#   obj
# }
